Bill had inimitable resilience. (When you reflect on what he went through during the impeachment saga, you have to sit down. It's too much. How could he, how did he, survive it? But he did, leaving office with an approval rating of more than 60%.) He was preternaturally cool under fire. And he was, of course, a brilliant President. At times he made it look easy. He ran a good economy, made big reforms, handled the Kosovo crisis with real leadership. It is fascinating to speculate how he would have handled later world-changing events, the whole crisis and sequence of tough decisionmaking that was started by the terrorist attacks of Sept. 11, 2001. There neither charm nor intellect would have been sufficient. It would have been pure caliber that determined the outcome. I believe he would have had it.

George Bush was straightforward and direct. And very smart. One of the most ludicrous caricatures of George is that he was a dumb idiot who stumbled into the presidency. No one stumbles into that job, and the history of American presidential campaigns is littered with political corpses of those who were supposed to be brilliant but who nonetheless failed because brilliance is not enough. To succeed in U.S. politics  or in the U.K.  you certainly have to be clever, otherwise you will be eaten alive; but you have to be more than clever. (See the top 10 across-the-pond duos.)

George has a sense of calm. I was in the White House on the evening of Sept. 20, 2001, with George just before he was to give his first speech to Congress after the terrorist attacks on New York and Washington nine days earlier. He was not panicking or fretting or even plain worrying. He was at peace with himself. He had his mission as President. He hadn't asked for it. He hadn't expected it. He hadn't found it. It had found him. But he was clear. The world had changed, and as President of the world's most powerful country, he was tasked with making sense of that change and dealing with it. I asked him if he was nervous. "No, not really," he replied. "I have a speech here, and the message is clear." I marveled at it, looked carefully at him; but, yes, he did appear to be completely at ease.

George had great intuition. But his intuition was less  as in the case of Bill  about politics and more about what he thought was right or wrong. This wasn't expressed analytically or intellectually. It was just stated. At times  since I was more from the Clinton school  I would find this puzzling, even alarming. I would be at a press conference with the President, in the epicenter of those world-changing events, and I would think, George, explain it; don't just say it.

However, over time, and more even in retrospect as events have continued to unfold after I left office, I have come to admire the simplicity, the directness, almost the boldness of George, finding in it strength and integrity. Sometimes, in the very process of reasoning, we lose sight of the need for a destination, for finding the way out of the labyrinth to solid ground that stands the test not of a few weeks, months or even a year or two, but of the vastness of the judgment of history.

Then there is Barack Obama, who stepped into the aftermath of the financial crisis and wars in Iraq and Afghanistan. And as if that weren't enough, he faces the challenges of avoiding a double-dip recession and preventing Iran from acquiring nuclear-weapons capability. As ever, with a new leader, the political character cannot be fully formed or comprehended immediately but happens over time. The personal character, however, is clear: this is a man with steel in every part of him. The expectation of his presidency was beyond exaggeration. The criticism is now exaggerated. He has remained the same throughout. And believe me, that is hard to do. I achieved that serenity only at the end.

I think I understand what the new President is trying to do. He is less opposed to some of the aims of the previous President than is supposed, or even politically convenient to admit. He is under no illusions as to the scale of the economic or security challenge and, in his own way, every bit as tough as George. He is trying to shape a different policy to meet these aims, avoiding market excesses in economics and the alienation of America from its allies, potential or actual, in meeting the security challenge.